 Chapter 5: Night time Flux correctionAubinet, Marc  ; ; Heinesch, Bernard et alin Aubinet, Marc; Vesala, Timo; Papale, Dario (Eds.) Eddy Covariance: A Practical Guide to Measurement and Data Analysis (2012) Detailed reference viewed: 19 (2 ULg)Eddy Covariance: A Practical Guide to Measurement and Data AnalysisAubinet, Marc ; ; Book published by Springer (2012) Detailed reference viewed: 231 (14 ULg)Uncertainty of carbon dioxide fluxes introduced by different high-pass filtering methods; ; Laffineur, Quentin et alConference (2009) Detailed reference viewed: 13 (5 ULg) Determinants of terrestrial ecosystem carbon balance inferred from European eddy covariance flux sites; ; et al in Geophysical Research Letters (2007), 34(1), Pioneering work in the last century has resulted in a widely accepted paradigm that primary production is strongly positively related to temperature and water availability such that the northern ... [more ▼] Pioneering work in the last century has resulted in a widely accepted paradigm that primary production is strongly positively related to temperature and water availability such that the northern hemispheric forest carbon sink may increase under conditions of global warming. However, the terrestrial carbon sink at the ecosystem level (i.e. net ecosystem productivity, NEP) depends on the net balance between gross primary productivity (GPP) and ecosystem respiration ( TER). Through an analysis of European eddy covariance flux data sets, we find that the common climate relationships for primary production do not hold for NEP. This is explained by the fact that decreases in GPP are largely compensated by parallel decreases in TER when climatic factors become more limiting. Moreover, we found overall that water availability was a significant modulator of NEP, while the multivariate effect of mean annual temperature is small and not significant. These results indicate that climate- and particularly temperature-based projections of net carbon balance may be misleading. Future research should focus on interactions between the water and carbon cycles and the effects of disturbances on the carbon balance of terrestrial ecosystems. [less ▲] Detailed reference viewed: 25 (1 ULg)On the separation of net ecosystem exchange into assimilation and ecosystem respiration: review and improved algorithm; ; et al in Global Change Biology (2005), 11(9), 1424-1439 This paper discusses the advantages and disadvantages of the different methods that separate net ecosystem exchange (NEE) into its major components, gross ecosystem carbon uptake (GEP) and ecosystem ... [more ▼] This paper discusses the advantages and disadvantages of the different methods that separate net ecosystem exchange (NEE) into its major components, gross ecosystem carbon uptake (GEP) and ecosystem respiration (R-eco). In particular, we analyse the effect of the extrapolation of night-time values of ecosystem respiration into the daytime; this is usually done with a temperature response function that is derived from long-term data sets. For this analysis, we used 16 one-year-long data sets of carbon dioxide exchange measurements from European and US-American eddy covariance networks. These sites span from the boreal to Mediterranean climates, and include deciduous and evergreen forest, scrubland and crop ecosystems. We show that the temperature sensitivity of R-eco, derived from long-term (annual) data sets, does not reflect the short-term temperature sensitivity that is effective when extrapolating from night- to daytime. Specifically, in summer active ecosystems the long-term temperature sensitivity exceeds the short-term sensitivity. Thus, in those ecosystems, the application of a long-term temperature sensitivity to the extrapolation of respiration from night to day leads to a systematic overestimation of ecosystem respiration from half-hourly to annual time-scales, which can reach > 25% for an annual budget and which consequently affects estimates of GEP. Conversely, in summer passive (Mediterranean) ecosystems, the long-term temperature sensitivity is lower than the short-term temperature sensitivity resulting in underestimation of annual sums of respiration. We introduce a new generic algorithm that derives a short-term temperature sensitivity of R-eco from eddy covariance data that applies this to the extrapolation from night- to daytime, and that further performs a filling of data gaps that exploits both, the covariance between fluxes and meteorological drivers and the temporal structure of the fluxes. While this algorithm should give less biased estimates of GEP and R-eco, we discuss the remaining biases and recommend that eddy covariance measurements are still backed by ancillary flux measurements that can reduce the uncertainties inherent in the eddy covariance data. [less ▲] Detailed reference viewed: 50 (4 ULg) |
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